The present invention is generally directed to an implantable medical device, e.g., a cardiac stimulation device, and is particularly directed to a method for treating tachycardia in a multi-chamber cardiac stimulation device.
Implantable cardiac stimulation devices are well known in the art. They include implantable pacemakers which provide stimulation pulses to cause a heart, which may beat too slowly or at an irregular rate, to beat at a controlled normal rate. They also include defibrillators, which detect when the atria and/or the ventricles of the heart are in fibrillation or a pathologic tachycardia and apply cardioverting or defibrillating electrical energy to the heart to restore the heart to a normal rhythm. Implantable cardiac stimulation devices may also include the combined functions of a pacemaker and a defibrillator.
The treatment and avoidance of ventricular fibrillation, is significant since without needed treatment, death may occur within minutes of an episode""s onset. It is estimated that such xe2x80x9csudden cardiac deathxe2x80x9d may result in 350,000 to 450,000 people per year, approximately one every minute. Tachycardia, i.e., an elevated cardiac rate typically in excess of 100 bpm (beats per minute), while potentially being symptomatic to the patient is generally not fatal. However, a tachycardia episode may accelerate either directly or via progression of the disease process into fibrillation and death may result. Therefore, it is desirable and potentially necessary to treat a tachycardia episode to avoid such a fatal progression.
While cardioversion or defibrillation therapy can be used, devices that can do such therapy, e.g., implantable cardioverter defibrillators (ICDs), are generally larger, costlier, and have shorter operational lives due to a larger power consumption. Additionally, the pain to the patient will generally be significant if the patient is awake. Accordingly, even with an ICD, a lower voltage, xe2x80x9cpainlessxe2x80x9d treatment referred to as anti-tachycardia pacing (ATP) may be used, at least as a first stage treatment. With ATP, one or more pacing pulses (typically a train of pacing pulses) are applied to a single chamber, typically the right ventricle or right atrium, where the tachycardia is sensed. The ATP pulses are generally applied synchronous to the detected tachycardia and at an accelerated rate. This type of treatment has been shown to be effective of terminating the tachycardia episode. However, should this single chamber ATP fail, treatment may need to be accelerated to cardioversion or defibrillation.
While cardiac stimulators, i.e., pacemakers and ICDs, with dual chamber, i.e., right atrium and right ventricle, sensing and pacing capabilities are well known, it is only in recent years that the industry has begun exploring devices that could sense and pace three or four chambers of the patient""s heart. However, it is believed that this exploration has not addressed the consequences of the use of such devices in treating tachycardia.
Therefore, what is needed is a system that can provide an improved ATP technique for treating a tachycardia that is suitable for a multi-chamber environment.
The present invention provides an improved system and method for performing multi-chamber anti-tachycardia pacing (ATP) in response to a tachycardia that is of particular use in an implantable cardiac stimulation device. The expected benefits of such a multi-chamber ATP include improved hemodynamic performance and the ability to terminate the tachycardia sooner. Embodiments of the present invention use an intrinsic chamber activation sequence and associated interchamber time delays, preferably automatically detected during a period of time when a pathologic tachycardia is not present, to treat a pathologic tachycardia should it occur. Such a device monitors two or more chambers of the patient""s heart, i.e., the controlled chambers, and in the event a tachycardia is detected, the device determines the chamber which originated the tachycardia. The device then selects an anti-tachycardia pacing (ATP) cycle length, typically a percentage of the detected tachycardia cycle length of the chamber where the tachycardia originated, and begins pacing the controlled chambers according to the intrinsic chamber activation sequence and interchamber delays (initially synchronized relative to a cardiac signal from the chamber which originated the tachycardia) at the ATP cycle length for a predefined period or until the tachycardia ends. Optionally, embodiments of the present invention may additionally include a hemodynamic sensor and may adaptively alter the activation sequence and/or interchamber time delays in response to feedback from the hemodynamic sensor.
A preferred implantable cardiac stimulation device configured for controlling a plurality of chambers of a patient""s heart through a plurality of electrodes implanted in electrical contact with each of the controlled chambers is comprised of a plurality of pulse generators (i.e., pacing circuits) each respectively configured for electrical coupling to at least one of the electrodes and configured to generate stimulation pulses to stimulate an associated chamber; a plurality of sensing circuits each respectively configured for electrical coupling to at least one of the electrodes and configured to receive intrinsic cardiac signals from an associated chamber; and a controller, coupled to the pulse generators and the sensing circuits, for detecting the presence of tachycardia from the received intrinsic signals and for determining which one of the chambers originated the tachycardia. When the controller detects tachycardia, a sequence of stimulation pulses is delivered according to calculated anti-tachycardia pacing cycle lengths to the controlled chambers relative to an intrinsic chamber activation sequence and associated interchamber time delays.
In a further aspect of the present invention, at least the initial delivery of the stimulation pulse sequence is synchronized relative to the chamber which originated the tachycardia, i.e., if the left atrium originated the tachycardia, then the left atrial pulse of the stimulation pulse sequence would be timed relative to the last intrinsic pulse that occurred in the originating chamber, i.e., the left atrium in this example.
In a next aspect of a preferred embodiment of the present invention, the intrinsic chamber activation sequence is periodically determined during periods of time when a pathologic tachycardia is not detected in any of the sensed chambers. When the stimulation pulse sequence is applied to terminate the tachycardia, it is preferably applied at an accelerated rate to attempt to terminate the tachycardia.
In a still further aspect of the present invention, a hemodynamic monitor may be used to monitor the performance of the patient""s heart in response to the aforedescribed therapy. While the therapy progresses, the applied activation sequence and/or its associated interchamber delays are adaptively modified in response to the output of the hemodynamic monitor to improve the heart""s performance during delivery of the aforedescribed therapy.